1. Field of the Invention
The present invention relates to a wire bonding method and apparatus for the same.
2. Prior Art
Heat and pressure as well as ultrasound are used for wire bonding. Today, however, ultrasound is almost always coused in the case of bonding by heat and pressure. In both cases, therefore, the bonding arm is made up with an ultrasonic vibrator and horn.
In the ultrasonic wire bonding method, as is well known, a bonding tool through which a wire is passed is brought to a first bonding point (e.g. a pad on a pellet) and a second bonding points (e.g. the lead post on a lead), so that the wire is connected to the first and second bonding points.
A heating block which heats semiconductor components that are to be bonded is installed beneath the bonding position. As a result, the horn which holds the bonding tool at one end is heated by radiant heat, resulting in that the horn elongates due to thermal expansion. Furthermore, since heat is generated when voltage is applied to the vibrator, the horn is heated also by this heat.
When the horn elongates, the bonding tool is not brought to predetermined bonding coordinates; a discrepancy occurs in the bonding position. For example, when the temperature rises from 20.degree. C. to 70.degree. C., the horn elongates by approximately 30 microns.
In conventional systems, the horn is cooled by air which is constantly blowing onto the horn so that the temperature rise of the horn is inhibited.
In the prior art as described above, the horn is cooled by air. However, since the difference between the temperature at the time the bonding work starts and the saturation temperature during the bonding operation is not reduced, repositioning must be performed when the saturation temperature is reached.